A. Field of the Invention
This invention relates generally to the subject of equipment used in manufacturing drawn and ironed cans, for example, aluminum beverage cans. More particularly, the invention relates to improvements in a redraw sleeve (sometimes referred to as a cup holder) that is used in a body maker or can forming station. The redraw sleeve has several novel features that help prevent wrinkles from forming in the bottom profile of the can as the redrawn cup is drawn and ironed in the body maker.
B. Description of Related Art
It is well known to draw and iron a sheet metal blank to make a thin-walled can body for packaging beverages, such as beer, fruit juice or carbonated beverages. In a typical manufacturing method for making a drawn and ironed can body, a circular disk or blank is cut from a sheet of light gauge metal (such as aluminum). The blank is then drawn into a shallow cup using conventional cup forming punch and die equipment.
The cup is then transferred to a body maker or can forming station. In the body maker, the cup is fed, e.g., by gravity, into the station and positioned over the end portion of a redraw sleeve such that the redraw sleeve fills the interior of the cup. The body maker draws and irons the side walls of the cup to approximately the desired height and forms dome or other features on the bottom of the can. In particular, a conventional body maker includes a punch adapted to move longitudinally within the interior of the redraw sleeve and force the cup through the redraw die and then through co-axially aligned ironing rings. As the punch forces the cup through the ironing rings, the side wall of the can is thinned. At the end of the punch travel, a bottom forming die cooperates with the head of the punch to produce a profile (typically a dome or similar structure) in the bottom wall of the can body.
As the above process is widely used in the aluminum beverage can industry, and therefore familiar to persons of ordinary skill in the art, it will not be described further herein. The general reader is directed to U.S. Pat. No. 4,852,377 and assigned to American National Can Co., the assignee of the present invention, and U.S. Pat. No. 3,735,629 for further details. Other representative patents relating to the same subject matter include U.S. Pat. No. 5,394,727 to Diekoff, U.S. Pat. No. 5,014,536 to Saunders, and U.S. Pat. No. 4,414,836 to Saunders. The above patents are incorporated by reference herein.
After formation of the can by the body maker, the top edge of the can is typically trimmed. The can is transferred to a necking station, where neck and flange features are formed on the upper region of the can. Necking stations are also well known in the art and the reader is directed to U.S. Pat. No. 4,774,839 to Caleffi et al. for a description of a representative necking station.
The present inventors have discovered that improvements to the form and shape of the redraw sleeve can significantly reduce the occurrence of wrinkle formation in the can body as the can is drawn and ironed. Prevention of wrinkles is significant, in that it permits the can forming line to work more efficiently and allows for the use of less material in the cans, reducing the cost of the can.
In particular, it has been noticed that when the cup is placed over the redraw sleeve and subsequently forced into the ironing rings by the punch, the cup side wall frequently tends to become distorted to form an oval shape in cross-section, instead of remaining substantially circular. This results in a pinching of the cup sidewall against the side portion of the redraw sleeve at opposite sides of the redraw sleeve. This phenomenon occurs due to the fact that the cup material possesses a grain or predetermined orientation, wherein the cup tends to flex or bend more easily in one direction (i.e., with the grain), and less easily in the opposite direction. The portions of the cup side wall with the grain tend to become bowed outwardly away from the redraw sleeve, whereas the portion of the cup side wall against the grain tend to become pinched against the side portion of the redraw sleeve. This pinching effect causes more drag between the walls of the cup and the redraw sleeve, resulting in uneven draw and occasional formation of wrinkles in the bottom profile of the redraw cup.
Cups are introduced into the body making station in a manner such that it is either impossible, or prohibitively expensive, to know in advance the direction of the grain of the cup and take corrective action to make the cup remain in an undistorted condition when it is placed over the redraw sleeve. The present inventors have designed an undercut feature in the redraw sleeve which will prevent this pinching or binding between the side walls of the can and the redraw sleeve, regardless of the orientation of the grain in the cup. The result is that the occurrence in wrinkling in the bottom of the redraw cup is reduced.
The present inventors have also discovered that the drawing and ironing process can be further improved by providing features in the redraw sleeve that promote the flow of metal between the closed end of the cup and the side walls of the cup during the drawing and ironing process. In particular, during the drawing and ironing process, the thickness of the closed end of the cup is reduced as metal flows between the face of the redraw sleeve and the redraw die, and into the side walls of the can. In accordance with another aspect of the invention, groove features in the face of the redraw sleeve (or other equivalent features to reduce the surface area thereof) improve the flow of metal around the rim and peripheral edge of the redraw sleeve, resulting in a reduction in the occurrence in wrinkles. A reduced outside radius on the face of the redraw sleeve causes the metal to be held tightly across the face of the punch nose, also resulting in a reduction in the occurrence of bottom wrinkling.